A method and device for removing heat-stable salts by electrodialysis

Abstract

The present invention relates to a method for removing heat-stable salt by electrodialysis, comprising the following steps: i) providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack comprising a cathode and an anode plate and at least one repeatable unit arranged between the two polar plates, an electric field being present between the cathode and the anode plates, and the repeatable unit comprising a "pure water channel-desalting channel-alkali solution channel" from the cathode plate to the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalting channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by an anion exchange membrane and an anion exchange membrane; ii) introducing pure water into the pure water channel, introducing raw water into the desalting channel, introducing alkali solution into the alkali solution channel, and iii) drawing out a product stream from the desalting channel; wherein the raw water comprises an organic amine compound and a heat-stable salt. The present invention utilizes an electrochemical reaction membrane stack to achieve the removal of heat-stable salt.

Description

Technical Field

[0001] The present application relates to a method and device for removing heat-stable salts by electrodialysis. Background Art

[0002] In the field of thermal power generation, carbon capture, utilization, and storage (CCUS) of CO2 generated by combustion is an effective countermeasure to mitigate the greenhouse effect. There are mainly the following methods for carbon capture of CO2: chemical absorption, physical adsorption, membrane separation, etc. Among these methods, the chemical absorption method using organic amine solution as the absorbent is the method with the largest application scale in industry at present.

[0003] In the process of recycling organic amine solution by the chemical absorption method, the organic amine solution that has absorbed CO2 undergoes a degradation reaction with the components in the flue gas in the regeneration tower, generating a series of heat-stable salts (HSS). Heat-stable salts are not easily decomposed in organic amine solution, and can cause corrosion of pipelines and equipment and reduce the CO2 absorption capacity of organic amine solution. Therefore, removing heat-stable salts from organic amine solution is the current research focus of the chemical absorption method. At present, the main methods for removing heat-stable salts from organic amine solution are distillation method, ion exchange method, and electrodialysis method. Among them, the distillation method has the disadvantage of high energy consumption. The ion exchange method requires a large amount of reagents to regenerate the resin column, with cumbersome operation and high cost. The electrodialysis method has relatively simple operation and is a method with relatively high acceptability at present.

[0004] The traditional electrodialysis method removes heat-stable salts by enabling the cations and anions of heat-stable salts to move directionally through the ion-selective membrane under the action of an electric field. The efficiency of removing heat-stable salts by this method is low, and the recovery rate of organic amine solution is low.

[0005] In recent years, there has been an improved electrodialysis method, which introduces hydroxide ions into the organic amine solution through the action of an electric field during the electrodialysis process, causing a chemical reaction between the heat-stable salts and the hydroxide ions, converting the bound amine in the heat-stable salts into organic amine compounds, thereby achieving the removal of heat-stable salts.

[0006] CN112495189A discloses a method for removing HSS in the DETA carbon capture process by three-compartment electrodialysis, which uses a membrane cell unit containing an anion exchange membrane - anion exchange membrane - cation exchange membrane arranged repeatedly to form corresponding alkali chambers, feed chambers, and salt chambers. The reaction process is that the protonated amine of the thermally stable salt in the feed chamber reacts with the hydroxide ions migrated from the alkali chamber to convert the bound amine into an organic amine compound. This method has a low efficiency in removing thermally stable salts, a low recovery rate of the organic amine solution, and a large amount of hydroxide ions migrating into the feed chamber during the reaction process will cause the pH value of the recovered organic amine solution to increase, which may cause new precipitation corrosion.

[0007] CN109758918A discloses a method for removing thermally stable salts in an organic amine solution for carbon dioxide capture by bipolar membrane electrodialysis. The reaction process is that the protonated amine of the thermally stable salt combines with the hydroxide ions generated by the bipolar membrane to form an organic amine compound. This method has a low efficiency in removing thermally stable salts, a low recovery rate of the organic amine solution, and a large amount of hydroxide ions entering the feed chamber during the reaction process will cause the pH value of the recovered organic amine solution to increase, which may cause new precipitation corrosion.

[0008] In summary, the electrodialysis methods for removing thermally stable salts in the prior art have various disadvantages.

[0009] Therefore, there is a need in the art for an electrodialysis method for removing thermally stable salts that can improve or overcome the above disadvantages. Summary of the Invention

[0010] In view of the above problems existing in the art, the present invention provides a method and device for removing thermally stable salts by electrodialysis.

[0011] The first aspect of the present application provides a method for removing thermally stable salts by electrodialysis, comprising the following steps:

[0012] i) Providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack comprising cathode and anode plates and at least one repeat unit disposed between the two plates, an electric field existing between the cathode and anode plates, the repeat unit comprising "pure water channel - desalination channel - alkali solution channel" from the cathode plate towards the anode plate, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalination channel being defined by a cation exchange membrane and an anion exchange membrane, and the alkali solution channel being defined by two anion exchange membranes;

[0013] ii) Introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali solution into the alkali solution channel, and

[0014] iii) Drawing out a product stream from the desalination channel;

[0015] Wherein,

[0016] The raw water contains organic amine compounds and heat-stable salts.

[0017] The second aspect of the present application provides an apparatus for removing heat-stable salts by electrodialysis, comprising:

[0018] - An electrochemical reaction membrane stack, which includes cathode and anode plates and at least one repeat unit disposed between the two plates. There is an electric field between the cathode and anode plates. The repeat unit includes "pure water channel - desalination channel - lye channel" from the cathode plate to the anode plate direction. The pure water channel is defined by an anion exchange membrane and a cation exchange membrane. The desalination channel is defined by a cation exchange membrane and an anion exchange membrane. The lye channel is defined by two anion exchange membranes;

[0019] - A drainage unit configured to introduce pure water into the pure water channel, introduce raw water into the desalination channel, introduce lye into the lye channel, and draw out a product stream from the desalination channel, wherein the raw water contains organic amine compounds and heat-stable salts.

[0020] The method and apparatus of the present invention utilize an electrochemical reaction membrane stack to respectively and directionally migrate the cations and anions of heat-stable salts to different channels, thereby achieving the removal of heat-stable salts from the organic amine solution. The method and apparatus of the present invention have high efficiency in removing heat-stable salts, high recovery rate of the organic amine solution, and since the migration of hydroxide ions to the organic amine solution is restricted during the removal process, the increase in the pH value of the recovered organic amine solution can be reduced or even avoided. Description of the Drawings

[0021] Figure 1 A schematic diagram of a repeat unit showing an embodiment of the present invention;

[0022] Figure 2 A schematic diagram showing the construction of a repeat unit from sub-repeat units in an embodiment of the present invention;

[0023] Figure 3 A schematic diagram of ion migration in a repeat unit showing an embodiment of the present invention;

[0024] Figure 4 A schematic diagram of ion migration in a repeat unit showing an embodiment of the present invention;

[0025] Figure 5 A schematic diagram of ion migration in a repeat unit showing an embodiment of the present invention;

[0026] Figure 6 A schematic diagram of ion migration in an example of an embodiment of the present invention;

[0027] Figure 7 The schematic diagram of ion migration in the comparative example of an embodiment of the present invention is shown. Detailed implementation manners

[0028] In order to make the invention object, technical solution and beneficial technical effects of the present application clearer, the present application will be described in detail below.

[0029] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] If there is no special instruction, all implementation manners and optional implementation manners of the present application can be combined with each other to form a new technical solution.

[0031] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0032] If there is no special instruction, all steps of the present application can be carried out sequentially, randomly, or simultaneously. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially, or steps (a) and (b) carried out simultaneously. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms used in this application have the same meanings as generally understood by those skilled in the art.

[0034] Unless otherwise specified, the operations mentioned in this application are carried out at room temperature and normal pressure.

[0035] Unless otherwise specified, the operations mentioned in this application can be implemented by means known to those skilled in the art.

[0036] Unless otherwise specified, the equipment, devices, instruments, parts, materials, medicaments, etc. mentioned in this application can be obtained by means known to those skilled in the art.

[0037] Unless otherwise specified, the indicators mentioned in this application, such as concentration, flow rate, current density, etc., can be measured by means known to those skilled in the art.

[0038] Term Definitions

[0039] In this text, the term "organic amine solution" refers to a solution containing organic amine compounds. In this text, organic amine compounds can also be referred to as organic amine molecules, denoted as Amin, which have reactivity with target substances (such as acidic gases). Organic amine compounds can be of types known to those skilled in the art, such as monoamines and polyamines, or for example primary amines, secondary amines, tertiary amines, or for example straight-chain amines, cyclic amines, and sterically hindered amines.

[0040] In this text, the term "organic amine ion" refers to a positively charged ion or group formed by the combination of an organic amine molecule and a proton (H + ), denoted as AminH + in this text, which does not have reactivity with target substances (such as acidic gases). Organic amine ions are positively charged and tend to move directionally in an electric field. Organic amine ions can exist in the form of a bound state as a component of a stable substance (referred to as "bound amine" in this text), or can exist in the form of a free state as free ions.

[0041] In this text, the term "heat stable salt (HSS)", or "heat stable salt" for short, refers to salts formed by the combination of organic amine compounds and absorbed acidic gases (such as CO2, etc.) that are not easily thermally decomposed. The cations constituting the heat stable salt are usually protonated organic amines (i.e., bound amines) formed by organic amine compounds, and the anions constituting the heat stable salt can have various types depending on the absorbed acidic gas, which are not restricted here.

[0042] In this text, the term "channel" refers to the space formed between the electrode plates and the adjacent ion exchange membranes, as well as between two adjacent ion exchange membranes in an electrochemical reaction membrane stack. It can be understood that in an electrochemical reaction membrane stack, there is a space between the electrode plates and the adjacent membranes, as well as between two adjacent membranes, rather than being in close contact. There can be various ways to name the channels. For example, the naming of the channels can be set according to the substances intended to be accommodated in the channels during the operation of the membrane stack. For instance, a "pure water channel" refers to the channel in the membrane stack designed to accommodate pure water; an "alkali solution channel" refers to the channel in the membrane stack designed to accommodate alkali solution; and an "electrolyte solution channel" refers to the channel in the membrane stack designed to accommodate electrolyte solution. Alternatively, the naming of the channels can be set according to the functions intended to be achieved in the channels during the operation of the membrane stack. For example, a "desalination channel" refers to the channel in the membrane stack designed to achieve the function of removing heat-stable salts. It can be understood that the naming set according to the accommodated substances or the achieved functions does not uniquely define the channels themselves, that is, a channel can be set with multiple names, and multiple channels can also be set with the same name.

[0043] The present invention provides a method for removing heat-stable salts by electrodialysis, comprising the following steps:

[0044] i) Providing an electrochemical reaction membrane stack, which includes cathode and anode plates and at least one repeat unit disposed between the two electrode plates. There is an electric field between the cathode and anode plates. The repeat unit includes a "pure water channel - desalination channel - alkali solution channel" from the cathode plate to the anode plate direction. The pure water channel is defined by an anion exchange membrane and a cation exchange membrane. The desalination channel is defined by a cation exchange membrane and an anion exchange membrane. The alkali solution channel is defined by two anion exchange membranes;

[0045] ii) Introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing alkali solution into the alkali solution channel, and

[0046] iii) Drawing out a product stream from the desalination channel;

[0047] Wherein,

[0048] the raw water contains organic amine compounds and heat-stable salts.

[0049] In a preferred embodiment of the present invention, the electrochemical reaction membrane stack can include multiple repeat units disposed between the two electrode plates, and the multiple repeat units are arranged in sequence.

[0050] In the present invention, the desalination channel is defined by the cation exchange membrane of the pure water channel and the anion exchange membrane of the alkali solution channel.

[0051] In a preferred embodiment of the present invention, the repeat unit consists of "pure water channel - desalination channel - lye channel", in other words, the repeat unit only includes "pure water channel - desalination channel - lye channel".

[0052] In a preferred embodiment of the present invention, the repeat unit includes "anion exchange membrane - cation exchange membrane - anion exchange membrane - anion exchange membrane" from the cathode plate to the anode plate direction.

[0053] In a preferred embodiment of the present invention, the membranes separating the channels in the repeat unit are composed of "anion exchange membrane - cation exchange membrane - anion exchange membrane - anion exchange membrane", in other words, the membranes separating the channels in the repeat unit only include "anion exchange membrane - cation exchange membrane - anion exchange membrane - anion exchange membrane" arranged in sequence.

[0054] In an embodiment of the present invention, the anion and cation exchange membranes included in the electrochemical reaction membrane stack of the present invention can be one or more anion and cation exchange membranes known to those skilled in the art, and they can be obtained or prepared in a manner known to those skilled in the art.

[0055] There are many types of ion exchange membranes. Most of the film-forming matrices are styrene - divinylbenzene copolymers, and there are also polyethylene, fluorine-containing polymers, polyvinylpyridine, etc. In terms of functional groups, the membrane body of the cation exchange membrane contains negatively charged acidic active groups, so it can selectively permeate cations and block anions. The membrane body of the anion exchange membrane contains positively charged basic active groups, so it can selectively permeate anions and block cations. The main ion exchange functional groups of the cation exchange membrane are: sulfonic acid group, phosphoric acid group, carboxylic acid group, phenolic group, and arsenate group and selenate group, etc.; the main ion exchange functional groups of the anion exchange membrane are amino group and arylamino group, etc.

[0056] Common preparation methods of ion exchange membranes include impregnation method, casting method, scraping method, etc. Among them, the scraping method is the main method for producing ion exchange membranes. This method is to dissolve or disperse a linear polymer without ion exchange functional groups in a mixture of olefin monomers that can introduce ion exchange groups and crosslinking agents, etc., and make it into a paste and scrape it on the reinforcing support mesh cloth, polymerize to obtain a base film, and then introduce ion exchange groups through a polymer chemical reaction to make an ion exchange membrane.

[0057] In one or more embodiments, the anion exchange membrane includes an anion exchange resin and a support mesh cloth, and the cation exchange membrane includes a cation exchange resin and a support mesh cloth.

[0058] The anion exchange resin for the anion exchange membrane is not particularly limited in principle, and those skilled in the art can select a suitable anion exchange resin according to actual needs. In one or more embodiments, the anion exchange resin can be selected from styrene-divinylbenzene copolymers and their derivatives modified with amino or arylamino groups. Preferably, the anion exchange resin can be a divinylbenzene-trimethylaminomethylstyrene chloride copolymer.

[0059] The cation exchange resin for the cation exchange membrane is not particularly limited in principle, and those skilled in the art can select a suitable cation exchange resin according to actual needs. In one or more embodiments, the cation exchange resin can be selected from styrene-divinylbenzene copolymers and their derivatives modified with sulfonic acid groups, phosphoric acid groups, carboxylic acid groups, phenolic groups, arsenic acid groups or selenic acid groups. Preferably, the cation exchange resin can be the sodium salt of a sulfonated divinylbenzene-styrene polymer.

[0060] In one or more embodiments, the support mesh for the ion exchange membrane can include one or more selected from polyolefins, fluoropolymers and polyesters.

[0061] In a preferred embodiment, the support mesh for the anion exchange membrane includes a polyolefin, and the support mesh for the cation exchange membrane includes a fluoropolymer.

[0062] When the support mesh for the anion exchange membrane includes a polyolefin and the support mesh for the cation exchange membrane includes a fluoropolymer, a better thermal stability salt removal effect can be achieved compared to using an ion exchange membrane containing a support mesh made of other materials.

[0063] In one or more embodiments, the polyolefin is selected from one or more of polyethylene and polypropylene. Preferably, the polyolefin can be polyethylene.

[0064] In one or more embodiments, the fluoropolymer is selected from one or more of homopolymers and copolymers of fluoroolefins. More preferably, the fluoropolymer can be selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and ethylene-tetrafluoroethylene copolymer. Further preferably, the fluoropolymer can be an ethylene-tetrafluoroethylene copolymer.

[0065] In a particularly preferred embodiment, the support mesh for the anion exchange membrane includes polyethylene, and the support mesh for the cation exchange membrane includes an ethylene-tetrafluoroethylene copolymer. More preferably, the support mesh for the anion exchange membrane can be composed of polyethylene, and the support mesh for the cation exchange membrane can be composed of an ethylene-tetrafluoroethylene copolymer.

[0066] Both the anion - exchange membrane and the cation - exchange membrane included in the electrochemical reaction membrane stack of the present invention can be commercially available products. As examples of the anion - exchange membrane, for instance, Selemion AMVN produced by Asahi Glass Co., Ltd. of Japan, ASE produced by ASTOM Corporation of Japan, AR103 of Veolia of France, FAS produced by Fumatech GmbH of Germany, and AME - Type12 produced by Fujifilm Corporation of Japan. Preferably, the anion - exchange membrane can be the anion - exchange membrane (AMVN) of Asahi Glass of Japan. As examples of the cation - exchange membrane, for instance, Selemion CMVN produced by Asahi Glass Co., Ltd. of Japan, CSE produced by ASTOM Corporation of Japan, CR61 of Veolia Corporation of France, FKS produced by Fumatech GmbH of Germany, and CME - Type12 produced by Fujifilm Corporation of Japan. Preferably, the cation - exchange membrane can be the cation - exchange membrane (CMVN) of Asahi Glass Co., Ltd.

[0067] The cathode and anode plates included in the electrochemical reaction membrane stack of the present invention can be one or more cathode and anode plates known to those skilled in the art, and they can be obtained or prepared in a manner known to those skilled in the art.

[0068] In one embodiment of the present invention, as Figure 1 shown, the electrochemical reaction membrane stack can include cathode and anode plates and a plurality of anion - exchange membranes (denoted as A membranes) and cation - exchange membranes (denoted as C membranes) disposed between the two plates. The "..." in the figure represents other ion - exchange membranes that may exist. The anion - exchange membrane and the cation - exchange membrane are parallel to the cathode and anode plates and are arranged in the following order from the cathode plate to the anode plate to form a repeat unit:

[0069] A membrane - C membrane - A membrane - A membrane.

[0070] For ease of description, within one repeat unit, it can also be written as:

[0071] The first A membrane - C membrane - the second A membrane - the third A membrane.

[0072] Among them, the pure - water channel is defined by the first A membrane and the C membrane, that is, the space between the first A membrane and the C membrane constitutes the pure - water channel; the desalination channel is defined by the C membrane and the second A membrane, that is, the space between the C membrane and the second A membrane constitutes the desalination channel; the alkali - solution channel is defined by the second A membrane and the third A membrane, that is, the space between the second A membrane and the third A membrane constitutes the alkali - solution channel.

[0073] When the repeat unit is described by the above structure, when multiple repeat units are arranged in sequence, adjacent repeat units can share the same anion exchange membrane. In other words, the A membrane that participates in forming the lye channel of the previous repeat unit can also serve as the A membrane that participates in forming the pure water channel of the next repeat unit. Taking two adjacent repeat units as an example, the arrangement of their ion exchange membranes can be:

[0074] The first A membrane - C membrane - the second A membrane - the third A membrane - C membrane - the fourth A membrane - the fifth A membrane.

[0075] Among them, "the first A membrane - C membrane - the second A membrane - the third A membrane" forms the previous repeat unit, and "the third A membrane - C membrane - the fourth A membrane - the fifth A membrane" forms the next repeat unit.

[0076] The electrochemical reaction membrane stack of the above - mentioned embodiment can also be described in other ways. For example, as Figure 2 shown, the electrochemical reaction membrane stack can include anode and cathode plates and multiple anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) arranged between the two plates. The "..." in the figure represents other ion exchange membranes that may exist. The repeat unit can be constructed using the following sub - repeat units:

[0077] A membrane - C membrane - A membrane.

[0078] For the convenience of description, within one sub - repeat unit, it can also be written as:

[0079] The first A membrane - C membrane - the second A membrane.

[0080] When the sub - repeat unit is described by the above structure, when multiple sub - repeat units are arranged in sequence, adjacent sub - repeat units do not share the same anion exchange membrane. Thus, two adjacent sub - repeat units can contain one repeat unit. Taking two adjacent sub - repeat units as an example, the arrangement of their ion exchange membranes can be:

[0081] The first A membrane - C membrane - the second A membrane - the third A membrane - C membrane - the fourth A membrane.

[0082] Among them, "the first A film - C film - the second A film" constitutes the previous sub - repeatable unit, and "the third A film - C film - the fourth A film" constitutes the subsequent sub - repeatable unit. In these two adjacent sub - repeatable units, there is a repeatable unit composed of "the first A film - C film - the second A film - the third A film". In other words, in this repeatable unit, the pure water channel is formed by the space between the "first A film - C film" of the previous sub - repeatable unit, the desalination channel is formed by the space between the "C film and the second A film" of the previous sub - repeatable unit, and the lye channel is formed by the space between the second A film of the previous sub - repeatable unit and the third A film of the subsequent sub - repeatable unit.

[0083] It can be understood that the repeatable unit including "pure water channel - desalination channel - lye channel" and the repeatable unit including "A film - C film - A film - A film" can be equivalent. The former focuses on the spatial structure of the repeatable unit, while the latter focuses on the framework structure of the repeatable unit.

[0084] It can be understood that the description that the repeatable unit is composed of "pure water channel - desalination channel - lye channel" or the repeatable unit is composed of "A film - C film - A film - A film" or similar descriptions does not exclude additional structures in the repeatable unit. That is, in addition to the structure of "pure water channel - desalination channel - lye channel" or "A film - C film - A film - A film", the repeatable unit can additionally have other structures, such as other channels, provided that the additional structures do not affect the implementation of the inventive concept of the present invention. Specifically, as long as the removal of heat - stable salts in the organic amine solution under the action of an electric field is achieved through the structure of "pure water channel - desalination channel - lye channel" or "A film - C film - A film - A film", the additional components and their combinations are all included in the scope of the present invention.

[0085] In the electrochemical reaction membrane stack, a pole liquid channel is formed between the electrode plate and the adjacent ion - exchange membrane. In one embodiment of the present invention, a salt solution (also called pole liquid) for providing an operating environment for the core components of the device during device operation can be introduced into the cathode and anode liquid channels. The pole liquid can be, for example, a sodium chloride solution or a sodium sulfate solution, preferably a sodium sulfate solution. The concentration of the pole liquid can be routinely determined by those skilled in the art. For example, a sodium sulfate solution with a concentration of 3% based on the total weight of the sodium sulfate solution can be used. The pole liquid preferably circulates between its corresponding supply unit and the pole liquid channel.

[0086] In one embodiment of the present invention, the ion - exchange membranes adjacent to the cathode and anode plates in the electrochemical reaction membrane stack can both be cation - exchange membranes. Such a setting can reduce or even avoid the entry of impurity ions (such as those brought by the pole liquid) into the system, improving the product purity. To achieve this purpose, other channels can be added on both sides of the repeatable unit in the electrochemical reaction membrane stack. For example, it can be as Figure 6Exemplarily, a desalination channel and an alkali solution channel are added between the cathode plate and the repeat unit, and a pure water channel is added between the anode plate and the repeat unit. In this way, the two ends of the electrochemical reaction membrane stack are respectively the desalination channel and the pure water channel, so that the ion exchange membranes adjacent to the cathode and anode plates in the electrochemical reaction membrane stack are cation exchange membranes.

[0087] In one embodiment of the present invention, the organic amine compound of the present invention is selected from one or more of the following substances: monoethanolamine (MEA), N-methyldiethanolamine (MDEA), diethanolamine (DEA), piperazine (PZ), diethylenetriamine (DETA), triethylenetetramine (TETA), 2-amino-2-methyl-1-propanol (AMP), N-aminoethylpiperazine, and 3-diethylaminopropylamine (DEAPA), etc. Monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, and N-aminoethylpiperazine are preferred.

[0088] In one embodiment of the present invention, the cation of the heat-stable salt is selected from one or more of the following substances: protonated monoethanolamine (MEA), N-methyldiethanolamine (MDEA), diethanolamine (DEA), piperazine (PZ), diethylenetriamine (DETA), triethylenetetramine (TETA), 2-amino-2-methyl-1-propanol (AMP), N-aminoethylpiperazine, and 3-diethylaminopropylamine (DEAPA); protonated monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, and N-aminoethylpiperazine are preferred; the anion of the heat-stable salt is selected from one or more of the following ions: formate, acetate, propionate, glycolate, chloride, sulfate, thiocyanate, thiosulfate, nitrate, nitrite, and oxalate; formate, acetate, glycolate, sulfate, oxalate, and chloride are preferred.

[0089] In one embodiment of the present invention, the raw water is an organic amine solution containing a heat-stable salt.

[0090] In a preferred embodiment of the present invention, the initial content of thermally stable salts in the raw water is 5000 to 20000 ppm by weight, preferably 5000 to 19000 ppm by weight, more preferably 6000 to 19000 ppm by weight, more preferably 7000 to 19000 ppm by weight, more preferably 7000 to 18000 ppm by weight, more preferably 8000 to 18000 ppm by weight, more preferably 8000 to 17000 ppm by weight, more preferably 8000 to 16000 ppm by weight, more preferably 8000 to 15000 ppm by weight, more preferably 8000 to 14000 ppm by weight, more preferably 8000 to 13000 ppm by weight, more preferably 8000 to 12000 ppm by weight, more preferably 9000 to 12000 ppm by weight, more preferably 10000 to 12000 ppm by weight, more preferably 10000 to 11000 ppm by weight, based on the total weight of the raw water, so as to achieve a better removal effect of thermally stable salts.

[0091] In a preferred embodiment of the present invention, the initial molar concentration C of thermally stable salts in the raw water S(HSS) is 0.25 to 1.05 mol / L, preferably 0.25 to 0.95 mol / L, more preferably 0.35 to 0.95 mol / L, more preferably 0.45 to 0.95 mol / L, more preferably 0.45 to 0.85 mol / L, more preferably 0.45 to 0.75 mol / L, more preferably 0.55 to 0.75 mol / L, more preferably 0.65 to 0.75 mol / L, based on the total volume of the raw water, so as to achieve a better removal effect of thermally stable salts.

[0092] In a preferred embodiment of the present invention, the raw water generally does not contain calcium ions, magnesium ions and barium ions, unless these ions are present in trace amounts. In the case where these ions are present in trace amounts in the raw water, their concentration is below 20 ppm by weight.

[0093] In a preferred embodiment of the present invention, the raw water generally does not contain iron ions and aluminum ions, unless these ions are present in trace amounts. In the case where iron ions are present in trace amounts in the raw water, their concentration is below 0.3 mg / L. In the case where aluminum ions are present in trace amounts in the raw water, their concentration is below 1 mg / L.

[0094] In a preferred embodiment of the present invention, the raw water is pretreated before entering the electrochemical reaction membrane stack of the present invention to remove unwanted impurity ions or limit the content of thermally stable salts within a desired range. The pretreatment can be a means known to those skilled in the art and implemented in a manner known to those skilled in the art, without particular limitation. For example, the pretreatment can be multi-stage filtration or concentration, etc.

[0095] In one embodiment of the present invention, pure water is synonymous with deionized water.

[0096] In one embodiment of the present invention, the lye contains sodium hydroxide and / or potassium hydroxide, preferably sodium hydroxide. In a preferred embodiment of the present invention, the lye is a sodium hydroxide solution.

[0097] In a preferred embodiment of the present invention, the lye is a sodium hydroxide solution, and its initial concentration is 0.80% to 3.2%, preferably 1.0% to 3.2%, more preferably 1.2% to 3.2%, more preferably 1.4% to 3.2%, more preferably 1.6% to 3.2%, more preferably 1.6% to 3.0%, more preferably 1.6% to 2.8%, more preferably 1.6% to 2.6%, more preferably 1.6% to 2.4%, more preferably 1.8% to 2.4%, more preferably 1.8% to 2.2%, more preferably 2%, by mass concentration, so as to achieve a better effect of removing thermally stable salts.

[0098] In a preferred embodiment of the present invention, the lye is a sodium hydroxide solution. During the electrochemical reaction, the alkali concentration in the lye channel does not exceed 3.2%, more preferably 3.1%, more preferably 3.0%, more preferably 2.9%, more preferably 2.8%, more preferably 2.7%, more preferably 2.6%, more preferably 2.5%, more preferably 2.4%, by mass concentration; the lowest is not less than 0.30%, preferably 0.35%, more preferably 0.40%, more preferably 0.45%, more preferably 0.50%, by mass concentration; so as to achieve a better effect of removing thermally stable salts.

[0099] In a preferred embodiment of the present invention, the initial molar concentration C of hydroxide ions in the lye S(OH-) is 0.20 to 0.80 mol / L, preferably 0.25 to 0.80 mol / L, more preferably 0.30 to 0.80 mol / L, more preferably 0.35 to 0.80 mol / L, more preferably 0.40 to 0.80 mol / L, more preferably 0.40 to 0.75 mol / L, more preferably 0.40 to 0.70 mol / L, more preferably 0.40 to 0.65 mol / L, more preferably 0.40 to 0.60 mol / L, more preferably 0.45 to 0.60 mol / L, more preferably 0.45 to 0.55 mol / L, more preferably 0.5 mol / L, based on the total volume of the lye, so as to achieve a better effect of removing thermally stable salts.

[0100] In a preferred embodiment of the present invention, the ratio C of the initial molar concentration of hydroxide ions in the lye to the initial molar concentration of thermally stable salts in the raw water S(OH-) / C S(HSS)is from 0.25 to 1.75, preferably from 0.25 to 1.65, more preferably from 0.25 to 1.65, more preferably from 0.25 to 1.55, more preferably from 0.25 to 1.45, more preferably from 0.25 to 1.35, more preferably from 0.25 to 1.25, more preferably from 0.25 to 1.15, more preferably from 0.35 to 1.15, more preferably from 0.45 to 1.15, more preferably from 0.45 to 1.05, more preferably from 0.45 to 0.95, more preferably from 0.45 to 0.85, more preferably from 0.55 to 0.85, more preferably from 0.65 to 0.85, more preferably from 0.65 to 0.75.

[0101] In a preferred embodiment of the present invention, during the electrochemical reaction, the highest molar concentration C of hydroxide ions in the lye channel H(OH-) does not exceed 0.80 mol / L, more preferably 0.775 mol / L, more preferably 0.75 mol / L, more preferably 0.725 mol / L, more preferably 0.70 mol / L, more preferably 0.675 mol / L, more preferably 0.65 mol / L, more preferably 0.625 mol / L, more preferably 0.60 mol / L, based on the total volume of the liquid in the lye channel; the lowest molar concentration C L(OH-) is not lower than 0.075 mol / L, preferably 0.0875 mol / L, more preferably 0.1 mol / L, more preferably 0.1125 mol / L, more preferably 0.125 mol / L, based on the total volume of the liquid in the lye channel; thereby a better thermal stable salt removal effect can be achieved.

[0102] In a preferred embodiment of the present invention, the method of the present invention further includes, during the electrochemical reaction, when the molar concentration of hydroxide ions in the lye channel decreases to not higher than 0.25 mol / L, preferably 0.20 mol / L, more preferably 0.15 mol / L, based on the total volume of the liquid in the lye channel, adding at least once an alkali (preferably sodium hydroxide) to increase the hydroxide ion concentration to not lower than 0.25 mol / L, more preferably 0.30 mol / L, more preferably 0.35 mol / L, more preferably 0.40 mol / L, more preferably 0.45 mol / L, more preferably 0.50 mol / L, more preferably 0.55 mol / L, based on the total volume of the liquid in the lye channel, thereby a better thermal stable salt removal effect can be achieved.

[0103] In an embodiment of the present invention, in the case of a repeat unit, the expected technical effects of the present invention can be achieved. Selecting a repeat unit to illustrate the basic reaction process, such as Figure 3Exemplarily, the electrochemical reaction membrane stack may include an anode and a cathode plate, and a plurality of anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) disposed between the two plates. "..." in the figure represents other ion exchange membranes that may exist. Pure water is introduced into the pure water channel, raw water is introduced into the desalination channel, and lye is introduced into the lye channel. The anion of the heat-stable salt in the raw water (denoted as [HSS] - )) migrates towards the anode through the anion exchange membrane under the action of an electric field; the cation of the heat-stable salt (i.e., the organic amine ion (denoted as AminH + ), which can also be called the bound amine when it is a component of the heat-stable salt) migrates towards the cathode through the cation exchange membrane under the action of an electric field. Thus, according to the method of the present invention, heat-stable salts can be removed through ion exchange membranes under the action of an electric field.

[0104] In a preferred embodiment of the present invention, when a plurality of repeat units are arranged in sequence, further preferred technical effects can be achieved. Three sequentially arranged repeat units are selected to illustrate the further reaction process. For example, Figure 4 Exemplarily, the electrochemical reaction membrane stack may include an anode and a cathode plate, and a plurality of anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) disposed between the two plates. "..." in the figure represents other ion exchange membranes that may exist. Pure water is introduced into the pure water channel, raw water (i.e., the desalination channel) is introduced into the raw water channel, and lye is introduced into the lye channel. The lye is, for example, a sodium hydroxide solution. Under the action of an electric field, the cations in the system (organic amine ions (AminH + ), sodium ions (Na + )) migrate towards the cathode, and the anions (the anion of the heat-stable salt ([HSS] - )) and hydroxide ions (OH - )) migrate towards the anode. Combining the action of the electric field and the restrictive action of the ion exchange membranes in each channel, the ion flow directions in each channel are summarized as follows:

[0105] Pure water channel: AminH + and OH - migrate in;

[0106] Raw water channel: AminH + and [HSS] - migrate out;

[0107] Lye channel: OH - migrates out, and [HSS] - migrates in.

[0108] Without being bound by any specific theory, it can be considered that the following reactions occur in the method of the present invention:

[0109] AminH + [HSS- ]+Na + OH - →Amin+H2O+Na + [HSS - ]

[0110] Without being bound by any particular theory, it can be assumed that in the pure water channel, the OH - The migration of AminH + Migrate from the original water channel to the pure water channel, while AminH in the original water channel + The migration of the raw water channel is beneficial to the [HSS] - The migration of heat-stable salt can achieve better removal effect.

[0111] Without being bound by any particular theory, it can be assumed that the OH - The concentration of OH has multiple effects on the removal of heat-stable salts, which are as follows: ① As mentioned above, OH - Migration into the pure water channel is beneficial to [HSS] - Migrate from the raw water channel, the higher OH in the alkali solution - concentration is conducive to promoting this process; ② On the other hand, the OH - With the [HSS] to be relocated - As negatively charged anions, the excessive OH - Concentration will inhibit [HSS] to a certain extent - Migration of OH in alkali solution; - The concentration of OH is positively correlated with the solution conductivity. - The concentration will lead to too low solution conductivity and too high system resistance, which will increase the energy consumption of the electrodialysis process and reduce the desalination efficiency. The inventors unexpectedly found that the reasonable control of OH in the alkali solution channel during the electrochemical reaction (for example, the early and late stages of the reaction) - The concentration is conducive to achieving better heat-stable salt removal effect.

[0112] Without being bound by any particular theory, it can be assumed that in the alkali solution channel, the [HSS] from the adjacent raw water channel - It can react with Na in the alkali channel + Coordination occurs, thereby alleviating the migration of [HSS] into the alkali channel - AminH migrated into the adjacent pure water channel + The attraction of AminH can reduce or even avoid the migration of AminH from the adjacent pure water channel. + Break through the restriction of anion exchange membrane and migrate further into the alkaline solution channel. +Try to remain in the pure water channel and react with the OH migrating into the pure water channel - to form Amin and H2O. Since the migration rate of OH - is greater than that of AminH + , there will be excess OH - relative to AminH + in the pure water channel, and finally a solution containing Amin and OH - is formed. This solution can be recycled as a by-product stream to further reduce the loss of organic amines.

[0113] It can be understood that as described above, in the case of only one repeat unit without additional structures, the present invention can achieve the expected technical effects; in the case of multiple repeat units, the present invention can achieve further preferred technical effects. Of course, in the case of only one repeat unit, by adding other structures, the above-mentioned further preferred technical effects can also be achieved. For example, as Figure 5 exemplarily shown, the electrochemically reactive membrane stack may include an anode and a cathode plate and a plurality of anion exchange membranes (denoted as A membranes) and cation exchange membranes (denoted as C membranes) disposed between the two plates. The "..." in the figure indicates other ion exchange membranes that may exist. An adjacent alkali solution channel is provided beside the pure water channel of the repeat unit, and an adjacent pure water channel is provided beside the alkali solution channel of the repeat unit. In this way, the additional adjacent alkali solution channel and pure water channel can help the repeat unit achieve further preferred technical effects (the principle of achieving this further preferred technical effect is described in the foregoing).

[0114] Compared with the existing three-compartment electrodialysis technology (refer to CN112495189A, which is incorporated herein by reference), the method of the present invention has better technical effects. The existing three-compartment electrodialysis (refer to CN112495189A) adopts a membrane structure of "cation exchange membrane - anion exchange membrane - anion exchange membrane - cation exchange membrane", which defines a membrane cell unit of "alkali chamber - feed chamber - salt chamber" (where the alkali chamber is used to accommodate the alkali solution; the feed chamber is used to accommodate the feed solution and achieve the desalination function; the salt chamber is used to accommodate deionized water and form a salt solution). Without being bound by any specific theory, it can be considered that in the electrodialysis process of this prior art, hydroxide ions migrate from the alkali chamber into the feed chamber and react with the heat-stable salt to form an organic amine compound, water, and a heat-stable salt anion, and the heat-stable salt anion migrates from the feed chamber into the salt chamber, thereby achieving the removal of the heat-stable salt. In this process, there are two problems:

[0115] (1) As the reaction progresses, too many hydroxide ions migrating into the feed chamber may cause an undesired increase in the pH value of the product stream;

[0116] (2) Due to the action of the electric field, the following processes actually exist simultaneously in the system: ① OH - migrates from the alkali chamber to the feed chamber; ② The OH that migrates to the feed chamber - further migrates to the salt chamber; ③ The anions of heat-stable salts migrate from the feed chamber to the salt chamber. In the same feed chamber, the existence of process ② will weaken the progress of process ③, that is, weaken the removal efficiency of the anions of heat-stable salts.

[0117] Compared with the above-mentioned prior art, the method of the present invention even inhibits OH - from entering the raw water (or called feed liquid), thus avoiding the above-mentioned disadvantages existing in the prior art, and thereby being able to maintain the pH stability of the feed liquid and improve the removal efficiency of heat-stable salts.

[0118] In one embodiment of the present invention, the pH value of the product stream obtained by the method of the present invention is not higher than that of the untreated raw water. In one embodiment of the present invention, the pH value of the product stream obtained by the method of the present invention is lower than that of the untreated raw water.

[0119] In one embodiment of the present invention, the method of the present invention further includes drawing out a by-product stream from the pure water channel. The by-product stream contains organic amine compounds and hydroxide ions, and the organic amine compounds contained in the by-product stream are selected from the organic amine compounds contained in the raw water. In this way, the organic amine compounds in the by-product stream can be recycled, thereby further reducing the loss of organic amines.

[0120] In a preferred embodiment of the present invention, the method of the present invention further includes optionally introducing the by-product stream into the desalination channel after concentration. The concentration step in the present invention can be carried out by using conventional concentration methods and equipment known to those skilled in the art. Concentration can improve the efficiency of treating the by-product stream and recycling the organic amine compounds therein for the second time. In some cases, a small amount of [HSS] - may exist in the by-product stream. Therefore, the by-product stream can be introduced into the desalination channel to remove [HSS] - and further purified to utilize the by-product stream.

[0121] In one embodiment of the present invention, the method of the present invention can be carried out continuously or intermittently. In one embodiment of the present invention, the method of the present invention further includes providing a pure water supply unit, a raw water supply unit, and an alkali solution supply unit. Further, the method of the present invention further includes circulating pure water between a pure water channel and the pure water supply unit, circulating raw water between a desalination channel and the raw water supply unit, and circulating the alkali solution between an alkali solution channel and the alkali solution supply unit. Specifically, the pure water from the pure water supply unit is introduced into one end of the pure water channel and flows along the channel, then is led out from the other end and recycled back to the pure water supply unit; the raw water from the raw water supply unit is introduced into one end of the desalination channel and flows along the channel, then is led out from the other end and recycled back to the raw water supply unit; the alkali solution from the alkali solution supply unit is introduced into one end of the alkali solution channel and flows along the channel, then is led out from the other end of the channel and recycled back to the alkali solution supply unit.

[0122] In one embodiment of the present invention, the method of the present invention further includes applying a voltage to the cathode and anode plates to generate an electric field. The cathode and anode plates of the electro-chemical reaction membrane stack are connected to an external power source, so as to provide an electric field for the membrane stack during the operation of the device, enabling the directional movement of anions and cations in the membrane stack.

[0123] In one embodiment of the present invention, the initial current density of the electro-chemical reaction membrane stack in the process of the method of the present invention is 55 - 130 A / m 2 , preferably 60 - 130 A / m 2 , more preferably 60 - 120 A / m 2 , more preferably 70 - 120 A / m 2 , more preferably 80 - 120 A / m 2 , more preferably 90 - 120 A / m 2 , more preferably 100 - 120 A / m 2 . Reacting within this range of initial current density is beneficial to improving the desalination efficiency.

[0124] In one embodiment of the present invention, the method of the present invention further includes maintaining the solution conductivity in the alkali solution channel between 20 - 115 mS / cm, preferably 25 - 115 mS / cm, more preferably 25 - 110 mS / cm, more preferably 25 - 105 mS / cm, more preferably 30 - 105 mS / cm, more preferably 30 - 100 mS / cm, more preferably 30 - 95 mS / cm. Maintaining the solution conductivity in the alkali solution channel within this range is beneficial to the ion migration rate, and thus beneficial to improving the desalination efficiency.

[0125] In one embodiment of the present invention, the method of the present invention further includes maintaining the operating temperature of the electrochemically reactive membrane stack at 5-35°C, preferably at 10-35°C, more preferably at 20-35°C, more preferably at 20-30°C, and even more preferably at 25-30°C. Reacting at this temperature is beneficial to balancing the ion migration rate and the equipment life, and thus is beneficial to improving the desalination efficiency and reducing equipment loss.

[0126] In one embodiment of the present invention, the flow rate of each channel of the electrochemically reactive membrane stack can be set in a manner known to those skilled in the art and is not particularly limited herein.

[0127] In one embodiment of the present invention, when the concentration of the heat-stable salt in the solution in the desalination channel is lower than 5000 ppm by weight, preferably 4500 ppm by weight, a product stream is withdrawn from the desalination channel. In this way, it is beneficial to balance the heat-stable salt removal effect and the loss of organic amine.

[0128] The present application also provides a device for electroosmotic desalination of heat-stable salts, including:

[0129] An electrochemically reactive membrane stack, which includes cathode and anode plates and at least one repeat unit disposed between the two plates. There is an electric field between the cathode and anode plates. The repeat unit includes a "pure water channel - desalination channel - lye channel" from the cathode plate to the anode plate direction. The pure water channel is defined by an anion exchange membrane and a cation exchange membrane. The desalination channel is defined by a cation exchange membrane and an anion exchange membrane. The lye channel is defined by two anion exchange membranes;

[0130] A drainage unit, which is configured to introduce pure water into the pure water channel, introduce raw water into the desalination channel, introduce lye into the lye channel, and withdraw a product stream from the desalination channel, wherein the raw water contains an organic amine compound and a heat-stable salt.

[0131] Corresponding to the object of the present invention, the device of the present invention uses an electrochemically reactive membrane stack to respectively and directionally migrate the cations and anions of the heat-stable salt to different channels, thereby realizing the removal of the heat-stable salt from the organic amine solution. The device of the present invention has a high efficiency in removing heat-stable salts, a high recovery rate of the organic amine solution, and since the migration of hydroxide ions to the organic amine solution is limited during the removal process, the increase in the pH value of the recovered organic amine solution can be reduced or even avoided.

[0132] The descriptions of the equipment or devices involved in the above method are applicable to the corresponding descriptions of the device of the present invention.

[0133] In one embodiment of the present invention, the electrochemically reactive membrane stack may include a plurality of repeat units disposed between the two plates, and the plurality of repeat units may be arranged in sequence.

[0134] In one embodiment of the present invention, the drainage unit may also be configured to draw out a by-product stream from the pure water channel. The by-product stream contains an organic amine compound and hydroxide ions. In this way, the organic amine compound in the by-product stream can be recycled, thereby further reducing the loss of the organic amine compound.

[0135] In one embodiment of the present invention, the drainage unit may also be configured to introduce the by-product stream into the desalination channel after optionally concentrating it. In this way, the by-product stream can be introduced into the desalination channel to - remove [HSS], and further purified to utilize the by-product stream and reduce the loss of the organic amine compound.

[0136] In one embodiment of the present invention, the device of the present invention may also include a concentration unit. The concentration unit includes but is not limited to electrodialysis, forward osmosis, and high-pressure membranes. The concentration unit may be configured to concentrate the by-product stream. In this way, the efficiency of treating the by-product stream and secondarily recycling the organic amine therein can be improved.

[0137] In one embodiment of the present invention, the device of the present invention may also include a pure water supply unit, a raw water supply unit, and an alkali solution supply unit. The drainage unit may also be configured to circulate pure water between the pure water channel and the pure water supply unit, circulate raw water between the desalination channel and the raw water supply unit, and circulate the alkali solution between the alkali solution channel and the alkali solution supply unit.

[0138] In one embodiment of the present invention, the device of the present invention may also include an external power source, which is configured to apply a voltage on the cathode and anode plates to generate an electric field.

[0139] In one embodiment of the present invention, the drainage unit may also be configured to draw out a product stream from the desalination channel when the concentration of the heat-stable salt of the organic amine ion in the solution in the desalination channel is lower than 5000 ppm by weight, preferably 4500 ppm by weight. In this way, it is beneficial to balance the heat-stable salt removal effect and the loss of the organic amine.

[0140] In one embodiment of the present invention, the drainage unit of the present invention may also include a pump, preferably a metering pump, for introducing each material stream into the corresponding channel and maintaining the circulation of each material stream between the corresponding channel and the supply unit. Examples

[0141] The starting content is 11000 ppm by weight (starting molar concentration is approximately 0.7 mol / L). The pH of the raw water is 9.45. 2 L of NaOH solution (starting mass concentration is 2%) is introduced from the alkali solution supply unit into each alkali solution channel, and the alkali solution is circulated between each alkali solution channel and the alkali solution supply unit. 2 L of pure water is introduced from the pure water supply unit into each pure water channel, and the pure water is circulated between each pure water channel and the pure water supply unit. 3 L of sodium sulfate solution (mass concentration is 3%) is introduced into the bipolar solution channel.

[0142] The operating temperature of the electrochemical reaction membrane stack is maintained at 25 °C; the intermembrane voltage of the electrochemical reaction membrane stack is set to 6 V, and the starting current density of the electrochemical reaction membrane stack at this intermembrane voltage is 120 A / m 2 。

[0143] Turn on the external power supply and run the device for 180 minutes.

[0144] Monitor the conductivity of the NaOH solution in the alkali solution channel. Before the reaction starts, the conductivity of the 2% NaOH solution by mass is 93 mS / cm. When the device runs to the 90th minute, 35 g of NaOH solid is added. At this time, the mass concentration of the NaOH solution in the alkali solution channel increases from 0.6% to 2.35%, and the solution conductivity increases from 28.69 mS / cm to 104.3 mS / cm. After the reaction ends, the conductivity of the NaOH solution in the alkali solution channel is 49.3 mS / cm.

[0145] During the operation of the device, as the reaction progresses, the conductivity of the solution in the alkali solution channel changes, resulting in a change in the current density. Record the starting current density at the beginning of the experiment and the current density at the end of the experiment. Detect the pH value of the product stream. Detect the contents of various organic amine compounds, thermally stable salt cations (i.e., ions of various organic amine compounds), and anions in the product stream by ion chromatography. It should be noted that in ion chromatography, various organic amine compounds and their ions are represented as peaks of the same type. For example, 2-amino-2-methyl-1-propanol and its ion (i.e., protonated 2-amino-2-methyl-1-propanol) jointly appear as a peak a in the chromatogram, while monoethanolamine and its ion (i.e., protonated monoethanolamine) jointly appear as another peak b in the chromatogram. Add the mass concentrations of various organic amine compounds and thermally stable salt cations (i.e., ions of various organic amine compounds) and record it as the total mass concentration of organic amines in the product stream. Add the contents of various thermally stable salt anions and record it as the content of thermally stable salts in the product stream. Calculate the mass of organic amines in the raw water and the product stream respectively according to their mass concentrations of organic amines, and further calculate the amine recovery rate based on the mass of organic amines in the raw water before the experiment and the mass of organic amines in the product stream after the experiment. The calculation formula is as follows:

[0146] η = (m aA / m bA ）×100%

[0147] m aA : The mass of organic amine in the raw water (i.e., the product material stream) after the experiment;

[0148] m bA : The mass of organic amine in the raw water before the experiment.

[0149] Example 2

[0150] Operate according to Example 1, with the difference that a NaOH solution with a mass concentration of 1% is used. Before the start of the reaction, the conductivity of the NaOH solution with a mass concentration of 1% is 48 mS / cm. When the device runs to the 40th minute, 80th minute, 120th minute, and 160th minute, add 15 grams of NaOH solid each time. When adding for the first time, the mass concentration of the NaOH solution in the lye channel increases from 0.5% to 1.25%, and the solution conductivity increases from 27.87 mS / cm to 41.76 mS / cm; when adding for the second time, the mass concentration of the NaOH solution in the lye channel increases from 0.6% to 1.35%, and the solution conductivity increases from 29.93 mS / cm to 42.18 mS / cm; when adding for the third time, the mass concentration of the NaOH solution in the lye channel increases from 0.6% to 1.35%, and the solution conductivity increases from 28.55 mS / cm to 41.55 mS / cm; when adding for the fourth time, the mass concentration of the NaOH solution in the lye channel increases from 0.5% to 1.25%, and the solution conductivity increases from 31.21 mS / cm to 45.38 mS / cm. After the reaction ends, the conductivity of the NaOH solution in the lye channel is 41 mS / cm.

[0151] Example 3

[0152] Operate according to Example 1, with the difference that a NaOH solution with a mass concentration of 3% is used. Before the start of the reaction, the conductivity of the NaOH solution with a mass concentration of 3% is 138 mS / cm. When the device runs to the 130th minute, add 10 grams of NaOH solid. At this time, the mass concentration of the NaOH solution in the lye channel increases from 0.6% to 1.1%, and the solution conductivity increases from 30.32 mS / cm to 47.63 mS / cm. After the reaction ends, the conductivity of the NaOH solution in the lye channel is 39 mS / cm.

[0153] Example 4

[0154] Operate according to Example 1, with the difference that the intermembrane voltage is set to 4.5 V, and the initial current density of the electrochemical reaction membrane stack at this intermembrane voltage is 60 A / m 2 。

[0155] Example 5

[0156] Operate according to Example 1, with the difference that the intermembrane voltage is set to 5 V, and the initial current density of the electrochemical reaction membrane stack at this intermembrane voltage is 80 A / m 2 。

[0157] Example 6

[0158] Operate according to Example 1, with the difference that the operating temperature of the electrochemical reaction membrane stack is maintained at 5°C.

[0159] Example 7

[0160] Operate according to Example 1, with the difference that the operating temperature of the electrochemical reaction membrane stack is maintained at 15°C.

[0161] Example 8

[0162] Operate according to Example 1, with the difference that the initial content of heat-stable salts in the raw water used is 5697 weight ppm (initial molar concentration is about 0.3 mol / L), and the pH of this raw water is 9.91.

[0163] Example 9

[0164] Operate according to Example 1, with the difference that the initial content of heat-stable salts in the raw water used is 9218 weight ppm (initial molar concentration is about 0.5 mol / L), and the pH of this raw water is 10.05.

[0165] Example 10

[0166] Operate according to Example 1, with the difference that the initial content of heat-stable salts in the raw water used is 19105 weight ppm (initial molar concentration is about 1.0 mol / L), and the pH of this raw water is 9.54.

[0167] The parameters and their effect data (amine recovery rate, content of heat-stable salts in the product stream (which can be abbreviated as HSS), and pH of the product stream) of Examples 1 - 7 are summarized in Table 1 below.

[0168] Table 1:

[0169]

[0170] * C S(NaOH) (%) represents the initial mass concentration of NaOH, in mass %;

[0171] The starting molar concentration ratio of hydroxide ions in the lye of Examples 1-3, 8-10 to the starting molar concentration of heat-stable salts in the raw water and their effect data are summarized in Table 2 below.

[0172] Table 2:

[0173]

[0174] * C S(NaOH) (%) represents the starting mass concentration of NaOH, in mass %;

[0175] * C S(OH-) (mol / L) represents the starting molar concentration of OH - in mol / L;

[0176] * C S(HSS) (mol / L) represents the starting molar concentration of heat-stable salts, in mol / L.

[0177] The starting molar concentration of hydroxide ions in the lye of Examples 1-3, the change in molar concentration in the lye channel and their effect data are summarized in Table 3 below.

[0178] Table 3:

[0179]

[0180] * C S(NaOH) (%) represents the starting mass concentration of NaOH, in mass %;

[0181] * C NaOH (%) represents the real-time mass concentration of NaOH, that is, the mass concentration of the base in the lye channel, in mass %;

[0182] * C S(OH-) (mol / L) represents the starting molar concentration of OH - in mol / L;

[0183] * C OH- (mol / L) represents the real-time molar concentration of OH - in the lye channel, in mol / L;

[0184] Among them, the higher the amine recovery rate, the smaller the loss of organic amine. The lower the content of heat-stable salts, the higher the efficiency of removing heat-stable salts and the better the effect of removing heat-stable salts.

[0185] Without being bound by any specific theory, it can be considered that the hydrolysis or conjugation with water of the thermally stable salt anions present in the solution leads to a relative increase in the concentration of hydroxide ions, resulting in a relative increase in the pH value. After the experiment, the content of thermally stable salt anions in the product stream is reduced relative to the raw water, weakening the hydrolysis or conjugation that causes the pH value to increase, resulting in a slight decrease in the pH value of the product stream relative to the raw water. Comparative Example

[0186] Using the same materials and substances as in Example 1, the comparative example adopts the electrochemically reactive membrane stack configuration of the prior art, and its structure is as Figure 7 shown in the example, where the anion exchange membrane is represented as membrane A, and the cation exchange membrane is represented as membrane C; the desalination channel is represented as channel 1, the lye channel is represented as channel 2, the pure water channel is represented as channel 3, and the electrode solution channel is represented as channel 4. The "..." in the figure indicates the presence of other ion exchange membranes. The repeat unit of the comparative example consists of "lye channel - desalination channel - pure water channel" from the cathode plate to the anode plate direction, and the electrochemically reactive membrane stack of the comparative example includes 10 such repeat units.

[0187] Operating according to Example 1, it should be noted that when the intermembrane voltage of the comparative example is 6V, its initial current density is 210 A / m 2 .

[0188] The parameters and their effect data (amine recovery rate, thermally stable salt content, and pH of the product stream) of Example 1 and the comparative example are summarized in Table 4 below.

[0189] Table 4:

[0190]

[0191] * C S(NaOH) (%): represents the initial mass concentration of NaOH, in mass %.

[0192] It can be seen that compared with the comparative example, the loss of organic amine in Example 1 of the present invention is less; the efficiency of removing thermally stable salts is higher and the effect is better; the pH of the comparative example increases, while the pH of the product stream remains basically stable and there is no unexpected increase.

Claims

1. A method for removing heat-stable salts by electrodialysis, comprising the following steps: i) Providing an electrochemical reaction membrane stack, the electrochemical reaction membrane stack including cathode and anode plates and at least one repeat unit disposed between the two plates, an electric field existing between the cathode and anode plates, the repeat unit including "pure water channel - desalination channel - lye channel" from the cathode plate towards the anode plate direction, the pure water channel being defined by an anion exchange membrane and a cation exchange membrane, the desalination channel being defined by a cation exchange membrane and an anion exchange membrane, and the lye channel being defined by two anion exchange membranes; ii) Introducing pure water into the pure water channel, introducing raw water into the desalination channel, introducing lye into the lye channel, and iii) Drawing out a product stream from the desalination channel; wherein, the ion exchange membranes adjacent to the cathode and anode plates in the electrochemical reaction membrane stack are all cation exchange membranes; the raw water contains an organic amine compound and heat-stable salts, The initial molar concentration C of the heat-stable salts in the raw water S(HSS) is 0.7 mol / L, The initial molar concentration C of hydroxide ions in the lye S(OH-) is 0.50 mol / L, the ratio of the initial molar concentration of hydroxide ions in the lye to the initial molar concentration of heat-stable salts in the raw water is 0.71, during the electrochemical reaction, when the molar concentration of hydroxide ions in the lye channel decreases to no higher than 0.20 mol / L, based on the total volume of the liquid in the lye channel, adding lye at least once to increase the hydroxide ion concentration to no lower than 0.25 mol / L; During the electrochemical reaction, the highest molar concentration C of hydroxide ions in the lye channel H(OH-) does not exceed 0.80 mol / L, based on the total volume of the liquid in the lye channel; The initial current density of the electrochemical reaction membrane stack is 120 A / m 2 ; the operating temperature of the electrochemical reaction membrane stack is maintained at 25 °C.

2. The method according to claim 1, wherein the organic amine compound is selected from one or more of monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, and N-aminoethylpiperazine and its derivatives, and the heat-stable salts are composed of the following anions and cations: the cations of the heat-stable salts are selected from one or more of protonated monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, and N-aminoethylpiperazine; the anions of the heat-stable salts are selected from one or more of formate, acetate, glycolate, sulfate, oxalate, and chloride.

3. The method according to claim 1 or 2, wherein the desalination channel is defined by the cation exchange membrane of the pure water channel and the anion exchange membrane of the lye channel.

4. The method according to claim 1 or 2, wherein the lye is a sodium hydroxide solution.

5. The method according to claim 1 or 2, further comprising maintaining the solution conductivity in the lye channel between 20 - 115 mS / cm.

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